2. discriminator标签进行分类查询,感觉是为了实现继承类的ORMaping而存在的。
复合类型. User对象中包含一个Album列表. 注意collection标签中的column取值需要和User的sql中的列名对应,这里是user_id。取Album的sql中也用到这个列名:userid=#{user_id}
<resultMap type="User" id="userMapWithAlbum"> <id property="id" column="user_id" /> <result property="name" column="user_name" /> <result property ="sex" column="user_sex" /> <result property="age" column="user_age" /> <collection property="albums" column="user_id" ofType="Album" select="selectAlbumForUser" /> </resultMap> <select id="findById" parameterType="HashMap" resultMap="usermap"> select a.id as user_id, a.name as user_name, a.sex as user_sex, a.age as user_age from T_User a where a.id=#{id} </select> <select id="selectAlbumForUser" resultType="Album"> select * from T_Album where userId=#{user_id} </select>
分类应用,需要定义User的两个子类:GameUser和SingUser. GameUser有wins属性,SingUser有sings属性
<resultMap type="User" id="usermap"> <id property="id" column="user_id" /> <result column="user_name" property="name" typeHandler="example.dao.typehandler.SimpleTypeHandler"/> <result property ="sex" column="user_sex" /> <result property="age" column="user_age" /> <discriminator javaType="byte" column="user_sex"> <case value="1" resultType="example.model.GameUser"> <result property="wins" column="wins" /> </case> <case value="0" resultType="example.model.SingUser"> <result property="sings" column="sings" /> </case> </discriminator> </resultMap>